Photosensitive polymer composition for flexographic printing plates processable in aqueous media

ABSTRACT

A photocurable composition useful in preparing water-developable, solid printing plates is prepared by blending a urethane (meth)acrylate prepolymer with a complexing polymer based on poly(vinyl pyrrolidone) composition. The resulting composition is suitably formulated with additional photoactive (meth)acrylate monomers or oligomers and photoinitiator for casting or extrusion on a substrate to form a flexographic printing plate. Following UV exposure of the plate through a negative, unexposed areas can be removed by washing with aqueous media, to give a plate with a desirable relief image. The use of the aqueous washout solution as opposed to organic solvents minimizes pollution problems. The use of the complexing polymer significantly reduces the cold flow of the uncured plate and both increases toughness and reduces tack of the cured plate.

FIELD OF THE INVENTION

This invention relates to radiation curable formulations orcompositions, as well as photosensitive articles having solid surfacesor layers prepared from such polymers or formulations. Specifically,solid composition can be obtained by blending a liquid or semi-solidphotosensitive polymer having polar functionalities with a complexingpolymer. This blend is easily dispersible in aqueous media, yields anuncured material with good dimensional stability and a cured materialwhich is tough, yet relatively soft, and can be used to make a printingplate.

BACKGROUND OF THE INVENTION

Photocurable polymers and compositions are well known in the art forforming printing plates and other photosensitive or radiation sensitivearticles. In the field of radiation sensitive flexographic printingplates, the plates typically comprise a support and a photosensitivesurface or layer from a photocurable composition. Additional layers orsurfaces on the plate include slip and release films to protect thephotosensitive surface. Prior to processing the plate, the additionallayers are removed, and the photosensitive surface is exposed toradiation in an imagewise fashion. The unexposed areas of the surfaceare then removed in developer baths.

Removal of unexposed surfaces comprising solid photocurable compositionssuch as those disclosed in U.S. Pat. No. 2,760,863 require the use ofdeveloper baths comprising environmentally unsafe, organic solvents suchas tetrachloroethylene, 2-butanone, benzene, toluene, xylene,trichloroethane and solvent mixtures such astetrachloroethylene/n-butanol. However, due to the toxicity, highvolatility and low flash point, their use gives rise to hazardousconditions and creates pollution problems. Thus, recently there has beena strong interest in the field to develop photosensitive layers innon-organic solvent developing solutions, e.g., aqueous,surfactant-aqueous or alkaline-aqueous solutions. However, thecompositions resulting from recent attempts to achieve aqueousdevelopable plates demonstrate deficiencies in mechanical properties,e.g., flexibility. See European Application 261,910.

For instance, in addition to possessing an aqueous developablephotosensitive surface, a flexographic printing plate must havesufficient flexibility to wrap around a printing cylinder, yet be strongenough to withstand the rigors experienced during typical printingprocesses. Further, the printing plate should be soft enough tofacilitate ink transfer during printing.

Previous aqueous developable compositions have not possessed all thedesirable features such as flexibility, softness and solvent resistanceto inks typically used in printing. For example, U.S. Pat. No. 4,023,973describes a photosensitive composition comprising a maleic anhydrideadduct of a 1,2-polybutadiene. However, because the 1,2 content of thismaterial is very high, i.e., 70% or more, this composition has anundesirably high rubber hardness.

Furthermore, other water-developable photosensitive compositions whichcontain as the main component a high molecular weight polymer such aspolyvinyl alcohol, cellulose, polyethylene oxide, or the like, areinsufficient in flexibility and possess a high degree of rubber hardnessand hence are unsuitable for use in flexographic printing plates.

Finally, it is also important that the photosensitive surface of theprinting plate be dimensionally stable during storage. For example, somecompositions used for making plates have shown inferior stabilityproperties when used in solid flexographic printing plates in that thecompositions become tacky and pasty during storage. Those inferiorproperties have been attributed to the low molecular weight of thepolymers used to prepare the printing plates. See U.S. Pat. No.4,762,892 to Koch et al. and discussion of low molecular weight polymersdisclosed in Japanese Kokoku 57-23693.

Photosensitive formulations using the polymers of this invention arewater-developable without presenting any of the aforesaid disadvantages.

Certain polyurethane (meth)acrylate photosensitive polymers useful in anembodiment of the present invention are disclosed in copending U.S.application Nos. 924,264, filed Mar. 8, 1992 and 003,167, filed Dec. 1,1993, both of which are incorporated herein by reference as if set forthin full.

Toray Industries has two U.S. Pat. Nos. (4,889,793 and 4,927,739) and anEP Application (452,656) relate to water-developable flexographicprinting plates that use "gelling agents" in photosensitive compositionsbut do not specifically mention poly(vinyl pyrrolidone) polymers orcopolymers, and they contain only qualitative information with respectto physical properties.

P. Molyneux, "Water Soluble Polymers: Properties and Behavior", vol. II,pg. 171, CRC Press (1984) discusses the solubility in water ofhydrogen-bonding complexes.

SUMMARY OF THE INVENTION

In an embodiment of the present invention, a polyether diol(polyoxyalkylene diol) optionally with a polyester diol is end-cappedwith an excess of a diisocyanate, the resulting isocyanate cappedpolyurethane is chain-extended with a alkyldialkanolamine, and thechain-extended polymer is reacted with hydroxyalkyl(meth) acrylate toterminate the polymer chains with (meth)acrylates. One of ordinary skillin the art will recognize that, in addition to the polyether diols andthe polyester diols discussed above, various blends of diols may beutilized. The above-described photopolymers have polar functionalitieswhich can hydrogen bond with complexing polymers, such as the polymersand copolymers of poly(vinyl pyrrolidone) ("PVP"). When the liquid orsemi-solid photosensitive polymers are blended with complexing polymers,a solid with improved cold flow, that is, better dimensional stabilityis obtained. The final polymer product is photosensitive (photocurable)and can be formulated with photosensitizer and (meth)acrylate diluentsto make water-developable printing plates, photoresists, and the like.

Key features of the invention include (inter alia):

(1) The final product is a solid. This means there is no cold flow inthe formulated printing plates, which remain dimensionally and thermallystable.

(2) The photopolymer synthesis optionally uses an alkyl dialkanolamine,thereby integrating an amine into the polymer chain, resulting in waterdispersibility.

(3) The photopolymer has terminal (meth)acrylate groups for UVcurability.

(4) The blend of the photopolymer and the complexing polymer isdispersible in water.

(5) The cured photopolymer composition also has increased tensilestrength and elongation, which gives a very tough flexographic printingplate.

OBJECTS OF THE INVENTION

It is an object of the invention to prepare a novel, solidwater-dispersible polymer of predetermined sequentially designedstructure which can be crosslinked or cured by exposure to actinicradiation.

A further object is to make a water-developable storage-stableflexographic relief printing plate.

A still further object is to make a printing plate that can be developedin aqueous solutions that are harmless to the environment.

It is an object of the invention to provide a photosensitive articlecomprising a novel photocurable composition.

Another object is to provide an uncured flexographic printing plate withimproved dimensional stability.

Unless otherwise indicated the term "(meth)acrylate" means eitheracrylate or methacrylate.

Molecular weights are number average, M_(n), as determined by GelPermeation Chromatography using polystyrene standards.

DETAILED DESCRIPTION Complexing Polymers

It has been found that the addition of a complexing polymer or copolymerto the formulation of a urethane (meth)acrylate photopolymer results ina solid composition that is water dispersible. Preferred complexingpolymers are the polymers and copolymers of PVP. Such materials arecommercially available as PVP polymers having molecular weights of 5,000to 100,000. Polymers having molecular weights of about 10,000, 24,000and 40,000 are commercially available from Aldrich Chemical Company,Milwaukee, Wis. PVP-vinyl acetate copolymers are available as Luviskol™polymers from BASF Corp., Parsippany, N.J. Of those, the copolymershaving up to 40% vinyl acetate are preferred. When the complexingpolymer is used, the uncured plate has improved cold flow. A furtheradvantage is that surface tack, which can occur with certain unblendedphotosensitive polymers, is reduced.

Urethanes

The photosensitive polymers having polar functionality of one embodimentof the invention are polyurethane (meth)acrylates. Such materials can beprepared as described below. The main reactions and products involved inthe invention are given schematically and simplistically as follows:

1. P+Cy→(Cy--P)_(x) --Cy (I);

2. N+Cy→(Cy--N)_(y) --Cy (II);

3. I+N+II→[(Cy--P)_(x) --(Cy--N)_(y) ]_(z) --Cy (Prepolymer III, orIII): this reaction is optional;

(Note: Reactions 2. and 3. go forward together.)

4. III+A→A--[(Cy--P)_(x) --(Cy--N)_(y) ]_(z) --Cy--A (Photopolymer IV,or IV,

where P is a polyether diol or polyester diol or their moieties, Cy is adiisocyanate or its moiety, N is an alkyldialkanolamine or its moiety,and A is a hydroxyalkyl(meth)acrylate or its moiety. In these reactionshydroxyl containing compounds are linked to diisocyanate containingcompounds via urethane linkages, --NH--C(:O)--O--, to form therespective moieties. x, y, and z may differ from molecule to molecule,but are such that the over-all molecular weight of Prepolymer III,whether made from polyether diol or polyester diol or their mixtures, asin the range of about 5,000-60,000 (preferably about 5,000-30,000), andthat of Photopolymer IV is in the range of about 5,000-60,000(preferably about 7,000-40,000). Segments of I and II may be positionedrandomly in the chain.

The aforesaid 4 reactions may be restated explicitly. In thisrestatement the mole ratio of P:Cy:N:A must be 1:1.3-8:0.2-7:0.1-3,preferably 1.1.5-6:0.4-5:0.2-1.

Depending on the molecular weight of the polyols (in this casepolyether, polyester, polycaprolactone or polycarbonate polyols ormixtures of polyols), it is preferable to select the molar ratio of thereactants P (for polyols), Cy (for diisocyanate), N (foralkyldi-alkanolamine) and A for hydroxyalkyl(meth)acrylate such that:(weight percent as cited below is based on the total weight of the finalphotopolymer):

(a) the total polyol content is preferably between 60 and 80 weightpercent in order for the final photopolymer to have good flexibility orelastomeric properties and

(b) in one embodiment, the alkyldialkanolamine content is preferably1-10 weight percent in order to maintain good water developability,however use of alkyldialkanolamine is not required in all embodiments,and

(c) the hydroxyalkyl(meth)acrylate content is preferably 0.8-2 weightpercent so that good photocurability and hence good resistance to inkswell can be achieved.

1. Reaction of polyether or polyester diol (P) with the aforestatedstoichiometric excess of diisocyanate (Cy):

(i) In the case of polyether diol:

HO--(--A--O--)_(b) H+excess OCNR¹ NCO→OCN--B--R¹ --NCO (I-i)

where

A is --CH₂ CH₂ --, --CH₂ CH₂ CH₂ --, --CH₂ CH(CH₃)--, --CH₂ CH₂ CH₂ CH₂--, --CH₂ CH₂ CH(CH₃)--, or --CH₂ CH(CH₃)CH₂ -- or mixtures thereof;

B represents one or more segments of [--R¹ --NH--C(:O)O(--A--O--)_(b)C(:O)NH--]

b is determined by the molecular weight of the polyether diol and isdiscussed in the description of polyether diol, below.

R¹ is a divalent aromatic, aliphatic, or cycloaliphatic group containing2-20 carbons, preferably 5-15.

(ii) In the case of polyester diol:

HO--D--R² OH+excess OCNR¹ NCO→OCN--R¹ --E--NCO (I-ii)

where

D represents repeating segments of [--R² --O--C(:O)--[(R³)₀ or 1]--C(:O)O--],

E represents one or more segments of [--NHC(:O)--O--D--R²O--C(:O)--NH--R¹ --]

R² is a divalent aliphatic, cycloaliphatic, or alpharyl group of 2-20carbons;

R³, when present (i.e., when R³ is 1), is a divalent aliphatic,cycloaliphatic, aryl or alpharyl group of 1-22 carbons.

When mixtures of polyether diols and polyester diols are used, the diolscan be used in any ratio.

These end-capping reactions are well known. As indicated, the terminalisocyanates on initially formed end-capped diols may react with otherhydroxyl groups on other polyether or polyester diols, therebyincreasing over-all molecular weight of the resulting polyurethane. Thisreaction is suitably carried out at conventional temperatures, e.g.,within the range of about 25°-80° C.

Optional chain extension of prepolymer product (I-i and/or I-ii) withalkyldialkanolamine (HO--R⁴ --R⁵ --R⁶ --OH). In this operation,Reactions 2 and 3 go forward together, the product II of Reaction 2serving as an intermediate in Reaction 3:

2. OCN--R¹ --OCN+HO--R⁴ --R⁵ --R⁶ --OH→OCN--F--R¹ --NCO (II)

where

F represents one or more segments of [--R¹ --NH--C(:O)--O--R⁴ --R⁵ --R⁶--O--C(:O)NH--]

R⁴ and R⁶ are the same or different alkylene groups with 1-6 carbons; orR⁴ can be --(CH₂ CH₂ O)_(d) CH₂ CH₂ -- provided R⁶ is --(CH₂ CH₂ O)_(e)CH₂ CH₂ --, where d and e are each 0-9 and d+e=3-15;

R⁵ is --N(R⁷)--, -- N N--, or --N(Ph)--; Ph=phenyl)

R⁷ is an alkyl group with 1-6 carbons.

3. I+HO--R⁴ --R⁵ --R⁶ --OH+II→OCN--R--R¹ --NCO (Prepolymer III, or III),

where R comprises one or more segments of B and/or one or more segmentsof E; and one or more segments of F; which is to say, R comprises B, E,and F; or R consists essentially of B and F; or R consists essentiallyof B and E.

Reactions 2 and 3 are carried out in the same reaction mixturesubstantially simultaneously, at a temperature in the range of about25°-60° C., until all of the hydroxyl groups have reacted as determinedby titration of the remaining isocyanate. As indicated, individualpolymer chains in III may be expected to vary in the number of polyetherdiol, polyester diol, diisocyanate, and alkyldialkanolamine moieties.The reactant proportions are controlled within the ranges stated aboveso that all or substantially all polymer chains will terminate inisocyanate. This condition is essential for the fourth (and final) step.A small amount of residual free diisocyanate may be left after theformation of III.

In Reactions 2 and 3, note that the molar ratio, Cy/(P+N), is always >1.

Within III a preferred structure results when

R¹ is 4,4'-methylene diphenylene (MDI)

R⁴ and R⁶ are ethylene;

R⁵ is --N(R⁷)--;

R⁷ is methyl;

the diols include a mixture of an ethylene oxide end-cappedpolyoxypropylene diol and a polypropylene adipate diol where(--A--O--)_(b) has a molecular weight of about 1000-3500.

Prepolymer III and the herein described processes for synthesizing itare considered novel.

Reaction 4. Reaction of chain-extended polymer (Prepolymer III) withhydroxyalkyl(meth)acrylate to give Photopolymer IV:

III+HO--R⁸ --O--C(:O)--C(R⁹)=CH₂ →G--R--R¹ --G, (Photopolymer IV), where

G is CH₂ =C(R⁹)--C(:O)--O--R⁸ --O--C(:O)--NH--,

R⁸ is 1-7 carbon alkylene, and

R⁹ is H or methyl.

Within IV a preferred structure results when

R¹ is MDI;

R⁴, R⁶, and R⁸ are ethylene;

R⁷ and R⁹ are methyl;

R⁵ is --N(R⁷)--;

the diols include a mixture of an ethylene oxide end-cappedpolyoxypropylene diol and a polypropylene adipate diol where;(--A--O--)_(b) has a molecular weight of about 1000-3500.

The relationship of III and IV is readily evident in the structureJ--R--R¹ --J' where the J's are identical and are either --NCO (givingIII), or G (giving IV).

This Reaction 4 is suitably carried out at a temperature in the range ofabout 60°-80° C. and is conveniently carried out following chainextension Reactions 2 and 3, in the same vessel. Consistent with III,Segments B and/or E, and F may be positioned at random in the polymerchains of IV. As indicated, most of the molecules comprise multiplemoieties of polyether (and/or polyester) diol, end-capping diisocyanate,and chain-extending dialkanolamine, with all or substantially allpolymer molecules of IV being terminated with alkylene(meth)acrylate.

The reactions described above can be carried out without a solvent, butpreferably are carried out in an anhydrous organic solvent. Suitablesolvents include methyl ethyl ketone, methyl isobutyl ketone, toluene,and mixtures thereof. The solvents should have a boiling point in therange of 80°-120° C. for easy casting of films and evaporation ofsolvent.

The following is a further description of the reactants.

The Diol

(a) Polyether Diol.

This product has the structure HO--(A--O)_(b) H where A is a divalentradical of ethylene, propylene, isopropylene, butylene, isobutylene; andb is such that the number average molecular weight of the group[A--O]_(b), or of the polymer diol (which is substantially the samething) is within the range of about 650-7,000, preferably about1,000-3,500. Polypropylene oxide glycol, MW about 1,000-3,500, orpolypropylene oxide end-capped with ethylene oxide, where the amount ofethylene oxide is 1-50 weight percent, preferably 10-30 weight percent,of the overall molecular weight, MW about 1,000 to 7,000, preferably1,000-4,000, are especially preferred. In the instance where copolymersare used, the idealized structure for A(O)_(b) would be

--(CH₂ CH₂ O)_(x) --(CH₂ CH(CH₃)--O)_(y) --(CH₂ CH₂ O)_(z) -- where x+zand y are such that the ethylene oxide moiety represents about 1-50,preferably 10-30, weight percent of the overall polyol molecular weight.Such copolymers include POLY G55-37 (MW 2952, containing about 30 weightpercent of ethylene oxide), and POLY L 225-28 (MW 4000, containing about20 weight percent ethylene oxide); both available from Olin Corp. Thepolyether diol reactants may be made by processes well known in the artby reacting an alkylene oxide or mixtures of alkylene oxides with acompound having at least one active hydrogen atom, such as water;monohydroxylic alcohols such as ethanol and propanol; and dihydroxylicalcohols such as ethylene glycol and monoethyl ether of glycerine. Thepoly(oxyalkylene) products of such reactions will have linearoxyalkylene or oxyethylene-higher oxyalkylene chains, and such chainswill terminate with hydroxyl groups. Conventional potassium hydroxidecatalysts or double metal cyanide catalysts can be used.

(b) Polyester Diol.

As noted, the polyester diol, HO--D--R² OH, where D and R² have thevalues above given, may be used alone or in admixture with polyetherdiols. Suitable polyester diols include those made from dibasic acids orcaprolactones with an excess of glycol. The dibasic acids, which arepreferred, are those of the structure HO--C(:O)--[(R³)₀ or 1 ]--C(:O)OH,with an excess of glycol of the structure HO--R² --OH where R² and R³are as above defined.

The molecular weight of D (or of the polyester diol, which issubstantially the same thing) should be about 600-6,000, preferablyabout 1,000-3,500.

Suitable dibasic acids include those of the saturated series, i.e.,oxalic, malonic, succinic, glutaric, adipic, pimelic, suberic, and thelike. In this group, adipic acid is preferred. Aromatic dibasic acidsinclude phthalic and terephthalic acids. In lieu of the acid itself, theanhydride may be used, e.g., phthalic anhydride, or its ester may beused, e.g., methyl terephthalate. Acid mixtures may be used. When R³ iszero the acid is of course oxalic. When R³ is "1," R³ contains 1-20carbons and the subsequent dibasic acid contains 3-22 carbons.

Suitable glycols for making the polyester diol include the alkyleneglycols, e.g., ethylene glycol, propylene glycol, trimethylene glycol,the three butane diols, tetramethylene glycol, isobutylene glycol,pinacol, and the like, including their mixtures. The diol may have acycloalkane structure or alkyl aromatic structure.

Useful polyester diols made from adipic acid include poly(diethyleneadipate) diol, poly(ethylene adipate) diol, poly(propylene adipate)diol, poly(propylene/ethylene) adipate diol, poly(butylene adipate)diol, poly(ethylene/butylene adipate) diol, poly(neopentyl adipate)diol, poly(hexane/neopentyl) adipate diol, poly(hexane adipate) diol,polycaprolactone diols and the like or mixtures thereof.

Processes for making polyester diols are well known. See, for example,Encyclopedia of Polymer Science and Engineering, John Wiley & Sons(1988), 2d Ed., Vol. 12, pp. 28-42, especially pp. 33-34; and Vol. 13,pp. 259-261.

The Diisocyanate

A wide variety of diisocyanates is available for end-capping thepolyether diol. These diisocyanates can be aliphatic, cycloaliphatic, oraromatic, with the structure OCN--R¹ NCO. The divalent radical R¹contains in general 2 to 100 carbon atoms and may optionally carrynon-interfering substituents such as ether groups, ester groups,urethane groups, amido groups, urea groups, aryl groups, aliphaticgroups, cycloaliphatic groups, or halogen atoms. Modified diisocyanatesare also usable, In one preferred embodiment, glycol modifieddiphenylmethane diisocyanate are particularly effective. Examples ofsuitable diisocyanates include 4,4'-methylene diphenyl diisocyanate(MDI), modified MDI, such as MDI reacted with a polyether polyol,available as Isonate 2181 from Dow Chemical Co., and MDI prepolymers,2,4-tolylene diisocyanate (toluene diisocyanate), 2,6-tolylenediisocyanate, mixtures of the two latter isomers, dimer of 2,4-tolylenediisocyanate, p-xylene diisocyanate, m-xylene diisocyanate,1,5-naphthalene diisocyanate, 3,3'-dimethylbiphenyl-,4,4'-diisocyanate,hexamethylene diisocyanate, trimethylhexamethylene diisocyanate, lysinediisocyanate, isophorone diisocyanate,4,4'-methylenebis(cyclohexylisocyanate), methylcyclohexane-2,4 (or2,6)-diisocyanate, 1,3-(isocyanatomethyl)cyclohexane,m-tetramethylxylene diisocyanate, p-tetramethylxylene diisocyanate, andmixtures thereof.

Conventional urethane-forming catalysts may be used in the reactionswith diisocyanates. These catalysts include, e.g., organo-tin compoundssuch as dibutyl tin dilaurate and stannous octoate, organo-mercurycompounds, tertiary amines, and mixtures of these materials.

Alkyldialkanolamine

This material has the structure HOR⁴ R⁵ R⁶ OH, where the numbered R'sare as above defined. Within this group, methyldiethanolamine,bis(hydroxyethyl)piperazine, OHC₂ H₄ --N N--C₂ H₄ OH, andN,N'-Bis(2-hydroxypropyl)aniline, HO--CH(CH₃)CH₂ --N(Ph)--CH₂ CH(CH₃)OHare preferred. (Ph - phenyl.)

Hydroxyalkyl(meth)acrylate

This material has the structure HO--R⁸ OC(:O)--C(R⁹)═CH₂, where the R'sare as above defined. Within this structure hydroxyethylmethacrylate ispreferred.

Formulations with the Invention Photopolymer

The simplest formulation is the photopolymer and complexing polymer,plus an effective amount of photoinitiator. Such mixture can be solventcast, as is, or the solvent removed and the mixture extruded to create asolid photopolymerizable layer on conventional backing materials.However, for many commercial uses it will be found preferable toformulate or extend the photopolymerizable composition with about 1 to30% by weight of reactive (i.e., photoactive) monomer or oligomer, andmost preferably in the range of 5 to 15% by weight reactive monomer.Suitable reactive monomers or oligomers are those of the formula:

    (CH.sub.2 ═C(R.sup.9)--C(:O)--O--).sub.q --R.sup.10

where R⁹ is H or methyl, R¹⁰ is an organic moiety having a valence of q,and q is an integer.

Such reactive (meth)acrylate diluents include, but are not limited to,trimethylolpropane triacrylate, hexanediol diacrylate, 1,3-butyleneglycol diacrylate, diethylene glycol diacrylate, 1,6-hexanedioldiacrylate, neopentyl glycol diacrylate, polyethylene glycol 200diacrylate, tetraethylene glycol diacrylate, triethylene glycoldiacrylate, pentaerythritol tetraacrylate, tripropylene glycoldiacrylate, ethoxylated bisphenol-A diacrylate, propylene glycolmono/dimethacrylate, trimethylolpropane diacrylate,di-trimethylolpropane tetraacrylate, triacrylate of tris(hydroxyethyl)isocyanurate, dipentaerythritol hydroxypentaacrylate, pentaerythritoltriacrylate, ethoxylated trimethylolpropane triacrylate, triethyleneglycol dimethacrylate, ethylene glycol dimethacrylate, tetraethyleneglycol dimethacrylate, polyethylene glycol-200 dimethacrylate,1,6-hexanediol dimethacrylate, neopentyl glycol dimethacrylate,polyethylene glycol-600 dimethacrylate, 1,3-butylene glycoldimethacrylate, ethoxylated bisphenol-A dimethacrylate,trimethylolpropane trimethacrylate, diethylene glycol dimethacrylate,1,4-butanediol diacrylate, diethylene glycol dimethacrylate,pentaerythritol tetramethacrylate, glycerin dimethacrylate,trimethylolpropane dimethacrylate, pentaerythritol trimethacrylate,pentaerythritol dimethacrylate, pentaerythritol diacrylate,urethane-methacrylate or acrylate oligomers and the like which can beadded to the photopolymerizable composition to modify the cured product.Monoacrylates such as cyclohexyl acrylate, isobornyl acrylate, laurylacrylate and tetrahydrofurfuryl acrylate and the correspondingmethacrylates are also operable as reactive diluents, as well asmethacrylate oligomers such as epoxy acrylates, urethane acrylates, andpolyester or polyether acrylates.

Photoinitiators

The formulations comprising the novel materials of this inventionrequire a photoinitiator. A large number are available and useful.

Photoinitiators for the photopolymerizable composition and formulationscontaining the same include the benzoin alkyl ethers, such as benzoinmethyl ether, benzoin ethyl ether, benzoin isopropyl ether and benzoinisobutyl ether. Another class of photoinitiators are thedialkoxyacetophenones exemplified by 2,2-dimethoxy-2-phenylacetophenone,i.e., Irgacure®651 (Ciba-Geigy) and 2,2-diethoxy-2-phenylacetophenone.Still another class of photoinitiators are the aldehyde and ketonecarbonyl compounds having at least one aromatic nucleus attacheddirectly to the carboxyl group. These photoinitiators include, but arenot limited to benzophenone, acetophenone, o-methoxybenzophenone,acetonaphthalene - quinone, methyl ethyl ketone, valerophenone,hexanophenone, alpha-phenyl-butyrophenone, p-morpholinopropiophenone,dibenzosuberone, 4-morpholinobenzophenone, 4'-morpholinodeoxybenzoin,p-diacetylbenzene, 4-aminobenzophenone, 4'-methoxyacetophenone,benzaldehyde, alpha-tetralone, 9-acetylphenanthrene,2-acetylphenanthrene, 10-thioxanthenone, 3-acetylphenanthrene,3-acetylindone, 9-fluorenone, 1-indanone, 1,3,5-triacetylbenzene,thioxanthen-9-one, xanthene-9-one, 7-H-benz[de]-anthracen-7-one,1-naphthaldehyde, 4,4'-bis(dimethylamino)-benzophenone, fluorene-9-one,1'-acetonaphthone, 2'-acetonaphthone, 2,3-butedione, acetonaphthene,benz[a]anthracene 7.12 diene, etc. Phosphines such as triphenylphosphineand tri-o-tolylphosphine are also operable herein as photoinitiators.The photoinitiators or mixtures thereof are usually added in an amountranging from 0.01 to 5% by weight of the total composition.

Other Additives

The compositions may also contain other additives, which are known inthe art for use in photocurable compositions, e.g., antioxidants,antiozonants, plasticizers and UV absorbers. To inhibit prematurecrosslinking during storage of the prepolymer containing compositions ofthis invention, thermal polymerization inhibitors and stabilizers areadded. Such stabilizers are well known in the art, and include, but arenot limited to, hydroquinone monobenzyl ether, methyl hydroquinone, amylquinone, amyloxyhydroquinone, n-butylphenol, phenol, hydroquinonemonopropyl ether, phenothiazine, phosphites, nitrobenzene andphenolic-thio compounds, and mixtures thereof. Such additives are usedin an amount within the range of from about 0.01 to about 4% by weightof the prepolymer. These stabilizers are effective in preventingcrosslinking of the prepolymer composition during preparation,processing and storage.

UV light absorbers, or UV light stabilizers, can be used to adjust thephotospeed and, therefore, exposure latitude of the polymer material.Numerous materials will be apparent to those skilled in the art.

The most important light stabilizer classes are:2-hydroxy-benzophenones, 2-hydroxyphenyl benzotriazoles, hindered aminesand organic nickel compounds. In addition, salicylates, cinnamatederivatives, resorcinol monobenzoates, oxanilides, and p-hydroxybenzoates are used as well. These additives are used in the range ofabout 0.09 to about 4% by 10 weight of the prepolymer.

Tinuvin® 1130, a substituted hydroxyphenyl benzotriazole, available fromCiba-Geigy Corp., has been found to work exceptionally well.

The compositions also may contain up to about 50% by weight of an inertparticulate filler which is essentially transparent to actinic light.Such fillers include the organophilic silicas, bentonites, silica andpowdered glass. Such fillers can impart desirable properties to thephotocurable compositions and reliefs on printing plates containingthose compositions.

The compositions may also contain dye and/or pigment coloring agents.The colorants present in the photopolymer composition must not interferewith the imagewise exposure and should not absorb actinic radiation inthe region of the spectrum that the initiator, present in thecomposition is activatable.

The colorant may be chosen from among the numerous commerciallyavailable pigments and dyes. The coloring agent may be used in a solventsoluble form, or in the form of a dispersion. Where a particulatematerial is used, the particle size should be less than 5000 Angstroms.More preferably, the particles will be in the 200-3000 Angstrom range.

Although numerous pigments and dyes useful in the practice of thepresent invention will be apparent to those skilled in the art, a smallnumber of such materials are listed here.

Suitable pigments include the Microlith® series available fromCiba-Geigy. Especially preferred are the A3R-K and 4G-K materials.Suitable dyes include for example, Baso Blue 645 (C.I. Solvent Blue 4),Baso Blue 688 (C.I. Solvent Blue 81), Luxol Fast Blue MBSN (C.I. SolventBlue 38), Neopen Blue 808 (C.I. Solvent Blue 70), Orasol™ Blue 2GLN(C.I. Solvent Blue 48), Savinyl® Blue GLS (C.I. Solvent Blue 44),Savinyl Blue RLS (C.I. Solvent Blue 45), Thermoplast Blue 684 (C.I.Solvent Violet 13) and Victoria Blue BO (C.I. Solvent Blue 7). Blue andviolet are used in current applications but the color of the dye is notcritical. Other colors could offer advantages, including for example,resistance to fading.

The composition may also contain a plasticizer. Examples of plasticizersinclude: benzoates, phthalates, phosphates and sulfonamides. Dipropyleneglycol dibenzoate is the preferred plasticizer.

Formulations using the photopolymers of this invention include thefollowing (in parts by weight):

(1) Photopolymer, a polyurethane (meth)acrylate) about 50-100,preferably about 70-90;

(2) A mono-, di-, or multi-acrylate diluent, which can be a monomer oroligomer, about 0-25, preferably about 5-15;

(3) Photoinitiator, about 0.1-10, preferably about 0.5-2.0;

(4) Organic solvent, 0 to about 200, preferably about 10-50.

(5) stabilizers, UV absorbers and colorants, 0.1 to 10, preferably about1-4, total.

(6) Polyvinyl pyrrolidone) or copolymer of PVP with up to 40% vinylacetate, about 0.1 to 50, preferably about 4 to 20.

(7) A plasticizer compatible with both the photopolymer and PVP such asdipropylene glycol dibenzoate, about 1-20, preferably about 2-10.

Preparation of Plate

The photocurable composition can then be shaped and formed as a solidlayer of suitable thickness according to conventional solvent casting,i.e., dissolving the composition inca solvent, shaping the solution intoa film or plate and removing the solvent. Conventional extrusion,calendaring or hot press techniques can also be used. Solid layers ofthe photosensitive composition in the form of a film can be adhered tosupports such as those comprising polyester, nylon or polycarbonate.Other suitable supports include woven fabrics and mats., e.g., glassfiber fabrics or laminated materials made of, for example, glass fibersand plastics, and steel or aluminum coated plates. It is preferred thatthe supports are dimensionally stable and resistant to the washoutsolutions.

It is also usually necessary to protect photosensitive surfaces fromcontamination by dirt and dust during storage before being exposed andwashed. Such protection is accomplished by lamination or application ofa flexible protective cover sheet to the side of the photocurablecomposition opposite that of the support. In addition, the photocurablecompositions can sometimes be tacky and it is thus also desirable toapply a release film to the surface of the photosensitive layer beforeapplication of the coversheet. The release film consists of a thin,flexible and water soluble polymeric film and allows for intimatecontact between the surface of the photocurable composition opposite tothe support and an image-bearing negative applied to the surface.

Exposure and Development

Photosensitive articles comprising a support having a solid layer orsurface comprising the photocurable composition, e.g., solidflexographic printing plates, can then be processed by well-knowntechniques for imagewise exposure to actinic light. Preferably, thelight should have a wavelength of from about 230-450 microns. Exposureis through a negative placed between the light source and thephotosensitive surface. Suitable sources of light include Type RSsunlamps, carbon arc lamps, xenon arc lamps, mercury vapor lamps,tungsten halide lamps and the like.

Exposure periods depend upon the intensity of the actinic light,thickness of the plate and the depth of the relief desired on theprinting plate. Periods of from 1 to 20 minute exposures are preferred.

Development

After exposure and removal of the negative, the unexposed areas of thephotosensitive surface can be developed (removed) in aqueous washoutsolutions as herein described. This feature is particularly advantageousin that it avoids problems of disposing of washout solutions containingcommonly used organic solvents, such as chlorinated solvents, alcohols,or ketones. The washout solution should be slightly acidic and maycontain a surfactant. Dilute vinegar or citric acid solutions arepreferred. Useful acidic surfactants include sodiumalkylnaphthalene-sulfonate, sodium alkylbenzene sulfonate, sodium alkylether sulfate, polyoxyalkylated alkylaryl phosphate ester sodium saltand the like. Overall additive concentrations are suitably 0.1-5%. Washtemperature can vary from 25°-70° C. preferably at ambient temperature.Following washout, the plate may be post-exposed for further hardeningof the relief work.

EXAMPLES

The following examples illustrate without limiting the invention.

The raw materials used in the examples are described below:

    ______________________________________                                        Item       Description                                                        ______________________________________                                        TDI        Toluene (or tolylene) diisocyanate, 2,4                                       and 2,6-80/20 isomer mixture from                                             Aldrich Chemical Co., Inc.                                         Isonate 2181                                                                             Modified 4,4'-methylene diphenyl                                              diisocyanate from Dow Chemical Co.,                                           % NCO = 23.                                                        PPG 1025   Polypropylene oxide diol from Arco                                            Chemical Co.; MW = 1000.                                                      Polypropylene oxide/ethylene oxide diol                                       from Olin Corp., MW = 1000.                                        Poly G 55-112                                                                            Polypropylene oxide/ethylene oxide diol                                       from Olin Corp., MW = 1000.                                        Poly G 55-37                                                                             ethylene oxide end-capped polyoxy-                                            propylene diol, hydroxyl number = 37,                                         MW = 3000 from Olin Chemical Co.                                   POLY L 225-28                                                                            ethylene oxide end-capped                                                     polyoxypropylene diol, hydroxyl number =                                      28, MW = 4000, from Olin Corp.                                     S-108-46   Rucoflex S-108-46 is polypropylene                                            adipate diol from Ruco Polymer                                                Corporation, MW = 2400.                                            PVP        poly(vinyl pyrrolidone) of MW 10,000                                          from Aldrich Chemical Co.                                          Luviskol   PVP-vinyl acetate copolymers from BASF                                        Corp.                                                              Irganox 1520                                                                             2,4-bis[(octylthio)methyl]-o-cresol used                                      as stabilizer, from Ciba-Geigy Corp.                               Irgacure 651                                                                             2,2-dimethoxy-2-phenylacetophenone, from                                      Ciba-Geigy Corp.                                                   Sartomer 9035                                                                            ethoxylated trimethylolpropane                                                trimethacrylate from Sartomer Co.                                  Benzoflex 9-88                                                                           dipropylene glycol dibenzoate from                                            Velsicol Chemical Corp., Chicago, IL                               ______________________________________                                    

EXAMPLE 1

10 parts of poly(vinyl pyrrolidone) of MW 10,000 from Aldrich ChemicalCo. were dissolved in 10 parts of methyl ethyl ketone and 10 parts ofethanol by standing overnight in a 60° C. oven. To this solution, 50parts of a liquid methacrylated polyurethane (viscosity about 30,000cps) (based on polyols such as Rucoflex S-108-46 and Poly G 55-37 fromRuco Polymers and Olin Chemicals, respectively, tolylene diisocyanateand hydroxypropyl methacrylate) were added and mixed with low shear forone-hour. Also mixed in were 0.5 parts of2,2-dimethoxy-2-phenyl-acetophenone (photoinitiator). The complexedpolymer solution was deaerated and solvent-cast into a waxy materialthat did not flow. These solid films were exposed through an image to UVlight and then developed in 0.4% citric acid at room temperature with awash rate in excess of 5 mils/min. The cured film had a Shore A hardnessof 39.

EXAMPLE 2

15 parts of Luviskol (PVP-vinyl acetate copolymer from BASF Corp.) weredissolved in 15 parts of ethanol by standing overnight in a 60° C. oven.The copolymer solution was mixed with 50 parts of the methacrylatedpolyurethane described in Example 1 and with 0.5 parts of2,2-dimethoxy-2-phenylacetophenone. The complexed polymer solution wasdeaerated and solvent-cast into a waxy material that did not flow. Whenprocessed further as in Example 1, the imaged film washed in a 1%aqueous acetic acid solution at room temperature with a rate in excessof 3.5 mils/min. The cured film had a Shore A hardness of 47.

EXAMPLE 3 A. Synthesis of Polyurethane-methacrylate (Polymer Solution A)

A two-liter resin kettle equipped with an air powered stirrer, anitrogen purge and a thermowatch was charged with 100 grams (0.266moles) of Isonate 2181, 196.3 grams (0.066 moles) of POLY G 55-37 and54.1 grams (0.022 moles) of Rucoflex S-108-46. The mixture was heated to60° C. for about 2 hours under vigorous stirring and then the reactionwas allowed to react for another 16 hours at 35° C. The reaction mixturewas then heated to 60° C. for another 4 hours until an isocyanate endpoint of about 1 milliequivalent per gram was reached (as determined bystandard titration with dibutylamine). Then 382 grams of toluene and 85grams of methyl ethyl ketone were added to the reaction vessel followedby the addition of 18.5 grams (0.155 moles) of methyldiethanolamine. Thetemperature of the reaction was then raised to 35° C. The reaction wasallowed to proceed for another 3-4 hours until the titration indicatedthat 0.05 milliequivalents of isocyanate groups per gram of solutionremained. 5.8 grams (0.044 moles) of hydroxyethylmethacrylate and 7.5grams of Irganox 1520 were then added. The reaction mixture was allowedto stir for another 16 hours after which there was no detectableisocyanate groups on the IR spectrum. The resulting polymer solution(designated as Polymer A) was a transparent, slightly yellow, viscousmixture.

B. Formulation of Polymer Solution A with Poly(vinyl pyrrolidone)

Polymer Solution A was then mixed with a poly(vinyl pyrrolidone)solution (prepared by dissolving 10 parts of PVP in 50 partsisopropanol) using an air powered stirrer and the formulations aredescribed in Table 1. The formulations were cast into films to evaporatethe solvents and the properties were determined.

Melt flow was determined by a CS-127 Melt Indexer from Custom ScientificInstruments, Cedar Knolls, N.J. The melt flow was the amount of polymerextruded at 75° C. with a 10 kg. weight and calculated on a basis of 10minutes. The values reported are an average of three runs.

                  TABLE 1                                                         ______________________________________                                                     Formula-                                                                              Formula-  Formula-                                                    tion A  tion B    tion C                                         ______________________________________                                        Poly(vinyl pyrrolidone)                                                                      0      part   17   parts                                                                              26.5 parts                             solution (10 parts PVP in                                                     50 parts Isopropanol)                                                         Parts of PVP based on                                                                        0      part   2.5  parts                                                                              4    parts                             Total solids content                                                          POLYMER SOLUTION                                                                             250    parts  250  parts                                                                              250  parts                             A (prepared as described                                                      above)                                                                        Hexanediol dimethacrylate                                                                    2.2    parts  2.2  parts                                                                              2.2  parts                             Lauryl methacrylate                                                                          2.2    parts  2.2  parts                                                                              2.2  parts                             Irgacure 651   1.1    parts  1.1  parts                                                                              1.1  parts                             Melt Flow (grams/10 min)                                                                     11        2.2       0.35                                       Elongation (%).sup.(1)                                                                       745       875       930                                        Tensile strength (psi)                                                                       360       855       1365                                       Modulus (psi)  185       240       290                                        Shore A        34        45        52                                         Resilience     25        25        23                                         Washout rate in 0.25%                                                                        1.7       1.7       --                                         formic acid at room                                                           temperature.sup.(2)                                                           ______________________________________                                         .sup.(1) Properties measured from 20 mil dry films, exposed for 10 minute     .sup.(2) Washout determined using an A&V brush type of lab washout unit  

EXAMPLE 4 A. Synthesis of Polyurethane-methacrylate (Polymer Solution B)

A two-liter resin kettle was charged with: 80 grams (0.213 moles) ofIsonate 2181, 110 grams (0.0354) moles) of POLY G 55-37, and 145.2 grams(0.0354 moles) of Poly L 255-28 (from Olin Chemicals, prepared usingdouble metal cyanide catalysts to obtain low unsaturation and lowmonoalcohol content, as described in "Thermoplastic PolyurethaneElastomers Made From High Molecular Weight POLY-L Polyols" by C. P.Smith et al., J. Elastomers and Plastics, Vol. 24, p. 306, October1992). While purging with nitrogen, the mixture was heated to 70° C. forabout 6 hours under vigorous stirring. Heat was then turned off and thereaction was then allowed to proceed for another 16 hours at ambienttemperature. The reaction was titrated and an isocyanate end point of0.84 milliequivalents per gram was reached. 145 grams of toluene and 32grams of methyl ethyl ketone were added, while mixing. A solutioncontaining 14.8 grams (0.1241 moles) of methyldiethanolamine chainextender, 145 grams of toluene and 32 grams of methyl ethyl ketone wasadded. The reaction mixture was stirred vigorously while the temperaturewas maintained below 40° C. The reaction was allowed to proceed foranother 6 hours after which a significant increase in the viscosity canbe observed and an isocyanate content of 0.05 milliquivalents per gramof solution was left (as determined by titration). A solution containing72 grams of toluene, 16 grams of methyl ethyl ketone and 7.2 grams ofIrganox 1520 was added, while stirring, followed by 4.6 grams (0.035moles) of hydroxyethylmethacrylate. The reaction was allowed to proceeduntil the complete disappearance of the isocyanate peak at 2260 cm⁻¹ onthe IR spectrum. The resultant product was a transparent, viscous liquid(designated as Solution B).

B. Formulation of Polymer Solution B with Poly(vinyl pyrrolidone)

Polymer Solution B was then mixed with a poly(vinyl pyrrolidone)solution (prepared by dissolving 10 parts of PVP in 50 partsisopropanol) using an air powered stirrer and the formulations aredescribed in Table 2. The formulations were cast into films to evaporatethe solvents and the properties were determined.

                  TABLE 2                                                         ______________________________________                                                       Formulation A                                                                           Formulation B                                        ______________________________________                                        Poly(vinyl pyrrolidone)                                                                        0       part    16.3  parts                                  solution (10 parts PVP in                                                     50 parts Isopropanol)                                                         Parts of PVP based on Total                                                                    0       part    4     parts                                  solids content                                                                POLYMER SOLUTION A                                                                             150     parts   150   parts                                  (prepared as described above)                                                 Hexanediol dimethacrylate                                                                      1.3     parts   1.3   parts                                  Lauryl methacrylate                                                                            1.3     parts   1.3   parts                                  Irgacure 651     0.7     parts   0.7   parts                                  Dipropylene glycol dibenzoate                                                                  0       part    3.4   parts                                  Melt Flow (grams/10 min)                                                                       9.9         1.1                                              Elongation (%).sup.(1)                                                                         650         875                                              Tensile strength (psi)                                                                         375         900                                              Modulus (psi)    175         200                                              Shore A          40          45                                               Resilience       39          44                                               ______________________________________                                         .sup.(1) Properties measured from 20 mil dry films, exposed for 10 minute     .sup.(2) Washout determined using an A&V brush type of lab washout unit  

What is claimed:
 1. A printing plate comprising a support and a layer ofphotocurable composition thereon, where the composition comprises, inparts by weight:(a) about 50 to about 100 parts of a photocurablepolymer; (b) about 0.1 to about 50 parts of a complexing polymer whichis a polymer or copolymer of poly(vinylpyrrolidone); (c) 0 to about 25parts of (meth)acrylate diluents; (d) about 0.1 to about 10 partsphotoinitiator; (e) about 0.002 to about 8 parts of a stabilizer; (f)about 0.1 to about 20 parts of a plasticizer that is compatible withboth the photocurable polymer and the complexing polymer; wherein thephotocurable polymer (a) is an amine-containingpolyurethane-(meth)acrylate prepared by reacting together:(i) anaromatic diisocyanate with (ii) a polyether and/or a polyester diol ofmolecular weight about 600-7000 and (iii) an alkyldialkanolaminecontaining two hydroxyl groups and an alkyl group and (iv) ahydroxyalkylmethacrylate.
 2. The printing plate according to claim 1wherein the photocurable polymer is from about 70 to about 90 parts byweight, the complexing polymer is from about 4 to about 20 parts byweight, the diluent is from about 5 to about 15 parts by weight, thephotoinitiator is from about 0.5 to about 2 parts by weight, thestabilizer is from about 1 to about 4 parts by weight, and plasticizeris from about 2 to about 10 parts by weight.
 3. A printing platecomprising a support and a layer of photocurable composition thereon,where the composition comprises, in parts by weight:(a) about 50 toabout 100 parts of a photocurable polymer that is prepared by the methodcomprising the steps of:(i) reacting together in a solvent for thereactants, in the mole ratios stated, modified MDI, 12 moles; ethyleneoxide capped polypropylene oxide diol having a molecular weight of about3,000, 3 moles; polypropylene adipate diol having a molecular weight ofabout 2400, 1 mole; thereby end-capping the diols with isocyanate; (ii)optionally adding to the reaction mixture of (i); methyl diethanolamine,7 moles; continuing the reaction to chain extend the isocyanate-cappeddiols, thereby providing chain-extended isocyanate-capped diolsterminated in isocyanate groups; (iii) adding to the reaction of (ii),hydroxyethylmethacrylate, 2 moles, and continuing the reaction to reactthe terminal isocyanate groups of (ii) with the hydroxyl groups of thehydroxyethylmethacrylate; (b) about 0.1 to about 50 parts of acomplexing polymer which is a polymer or copolymer of poly(vinylpyrrolidone); (c) 0 to about 25 parts of a diluent selected from thegroup comprising polypropylene glycol monomethacrylate, diethyleneglycol dimethacrylate, hexanediol dimethacrylate, lauryl methacrylate,trimethylopropane trimethacrylate, ethoxylated trimethylolpropanetrimethacrylate, aromatic acrylated urethane oligomer, C₁₄ -C₁₅methacrylate monomer mixture or mixtures thereof; (d) about 0.1 to about10 parts photoinitiator; (e) about 0,002 to about 8 parts of astabilizer; and (f) about 0.1 to about 20 parts of a plasticizer that iscompatible with both the photocurable polymer and the complexingpolymer.
 4. The printing plate of claim 3 wherein the compositionfurther comprises: a ultra-violet radiation absorber which is asubstituted hydroxyphenyl benzotriazole, and a pigment having a particlesize of less than 5000 angstroms.
 5. A printing plate comprising asupport and a layer of photocurable composition thereon, where thecomposition comprises, in parts by weight:(a) about 50 to about 100parts of a photocurable polymer that is prepared by the methodcomprising the steps of:(i) reacting together in a solvent for thereactants, in the mole ratios stated, modified MDI, 12 moles; ethyleneoxide capped polypropylene oxide diol having a molecular weight of about3,000, 2 moles; ethylene oxide capped polypropylene oxide diol having amolecular weight of about 4000, 2 moles; thereby end-capping the diolswith isocyanate; (ii) optionally adding to the reaction mixture of (i);methyl diethanolamine, 7 moles; continuing the reaction to chain extendthe isocyanate-capped diols, thereby providing chain-extendedisocyanate-capped diols terminated in isocyanate groups; (iii) adding tothe reaction of (ii), hydroxyethylmethacrylate, 2 moles, and continuingthe reaction to react the terminal isocyanate groups of (ii) with thehydroxyl groups of the hydroxyethylmethacrylate; (b) about 0.1 to about50 parts of a complexing polymer which is a polymer or copolymer ofpoly(vinyl pyrrolidone); (c) 0 to about 25 parts of a diluent selectedfrom the group comprising polypropylene glycol monomethacrylate,diethylene glycol dimethacrylate, hexanediol dimethacrylate, laurylmethacrylate, trimethylolpropane trimethacrylate, ethoxylatedtrimethylolpropane trimethacrylate, aromatic acrylated urethaneoligomer, C₁₄ -C₁₅ methacrylate monomer mixture or mixtures thereof; (d)about 0.1 to about 10 parts photoinitiator; (e) about 0.002 to about 8parts of a stabilizer; and (f) about 0.1 to about 20 parts of aplasticizer that is compatible with both the photocurable polymer andthe complexing polymer.
 6. The printing plate of claim 5 wherein thecomposition further comprises: a ultra-violet radiation absorber whichis a substituted hydroxyphenyl benzotriazole, and a pigment having aparticle size of less than 5000 angstroms.
 7. A printing platecomprising a support and a layer of photocurable composition thereon,where the composition comprises, in parts by weight:(a) about 50 toabout 100 parts of a photocurable polymer that is prepared by the methodcomprising the steps of:(i) reacting together in a solvent for thereactants, in the mole ratios stated, modified MDI, 12 moles; ethyleneoxide capped polypropylene oxide diol having a molecular weight of about3,000, 1 moles; ethylene oxide capped polypropylene oxide diol having amolecular weight of about 4000, 3 mole; thereby end-capping the diolswith isocyanate; (ii) optionally adding to the reaction mixture of (i);methyl diethanolamine, 7 moles; continuing the reaction to chain extendthe isocyanate-capped diols, thereby providing chain-extendedisocyanate-capped diols terminated in isocyanate groups; (iii) adding tothe reaction of (ii), hydroxyethylmethacrylate, 2 moles, and continuingthe reaction to react the terminal isocyanate groups of (ii) with thehydroxyl groups of the hydroxyethylmethacrylate; (b) about 0.1 to about50 parts of a complexing polymer which is a polymer or copolymer ofpoly(vinyl pyrrolidone); (c) 0 to about 25 parts of a diluent selectedfrom the group comprising polypropylene glycol monomethacrylate,diethylene glycol dimethacrylate, hexanediol dimethacrylate, laurylmethacrylate, trimethylolpropane trimethacrylate, ethoxylatedtrimethylolpropane trimethacrylate, aromatic acrylated urethaneoligomer, C₁₄ -C₁₅ methacrylate monomer mixture or mixtures thereof; (d)about 0.1 to about 10 parts photoinitiator; (e) about 0.002 to about 8parts of a stabilizer; and (f) about 0.1 to about 20 parts of aplasticizer that compatible with both the photocurable polymer and thecomplexing polymer.
 8. The printing plate of claim 7 wherein thecomposition further comprises: a ultra-violet radiation absorber whichis a substituted hydroxyphenyl benzotriazole, and a pigment having aparticle size of less than 5000 angstroms.
 9. A printing platecomprising a support and a layer of photocurable composition thereon,where the composition comprises, in parts by weight:(a) about 50 toabout 100 parts of a photocurable polymer that is prepared by the methodcomprising the steps of:(i) reacting together in a solvent for thereactants, in the mole ratios stated, modified MDI, 12 moles; ethyleneoxide capped polypropylene oxide diol having a molecular weight of about4,000, 4 moles; thereby end-capping the diols with isocyanate; (ii)optionally adding to the reaction mixture of (i); methyl diethanolamine,7 moles; continuing the reaction to chain extend the isocyanate-cappeddiols, thereby providing chain-extended isocyanate-capped diolsterminated in isocyanate groups; (iii) adding to the reaction of (ii),hydroxyethylmethacrylate, 2 moles, and continuing the reaction to reactthe terminal isocyanate groups of (ii) with the hydroxyl groups of thehydroxyethylmethacrylate; (b) about 0.1 to about 50 parts of acomplexing polymer which is a polymer or copolymer of poly(vinylpyrrolidone); (c) 0 to about 25 parts of a diluent selected from thegroup comprising polypropylene glycol monomethacrylate, diethyleneglycol dimethacrylate, hexanediol dimethacrylate, lauryl methacrylate,trimethylolpropane trimethacrylate, trimethylolpropane trimethacrylate,ethoxylated trimethylolpropane trimethacrylate, aromatic acrylatedurethane oligomer, C₁₄ -C₁₅ methacrylate monomer mixture or mixturesthereof; (d) about 0.1 to about 10 parts photoinitiator; (e) about 0.002to about 8 parts of a stabilizer; and (f) about 0.1 to about 20 parts ofa plasticizer that is compatible with both the photocurable polymer andthe complexing polymer.
 10. The printing plate of claim 9 wherein thecomposition further comprises: a ultra-violet radiation absorber whichis a substituted hydroxyphenyl benzotriazole, and a pigment having aparticle size of less than 5000 angstroms.